feat(diagnostics): add configurable stuck-session warning threshold

src/config/types.base.ts

@@ -205,6 +205,8 @@ export type DiagnosticsConfig = {
   enabled?: boolean;
   /** Optional ad-hoc diagnostics flags (e.g. "telegram.http"). */
   flags?: string[];
+  /** Threshold in ms before a processing session logs "stuck session" diagnostics. */
+  stuckSessionWarnMs?: number;
   otel?: DiagnosticsOtelConfig;
   cacheTrace?: DiagnosticsCacheTraceConfig;
 };